What's different about Trump that's allowed him to undo in 3 years what took 30 to assemble? Is it because of the senate minority filibuster thing? Is this really the consequence of that mistake in hindsite?
A more exact answer
It's a combination of various things, perfect storm-wise and the reason Mitch McConnell and the rest of the GOP basically bent the knee to Trump and his base once they realized he had an actual freaking shot at winning the Presidency.
Under McConnell's leadership, the Senate did everything they could to stop Obama from filling empty Judge positions, even on the Supreme Court for the simple goal of keeping those slots open until a Republican took the White House. The more openings, the more conservative judges that a GOP President could nominate/McConnell and the Senate can approve. Giving the Federal Judiciary a conservative slant that will last decades and give the GOP the same sort of firewall the Democrats were desperately wanting to create for themselves by stacking the court with liberal judges.
This ties into the meltdown over the Supreme Court, which the Democrats were DESPERATE to flip this decade under Obama or Hillary. If you control the Supreme Court, you basically control the country since the Supreme Court can make law/irrevocably kill laws with impunity due to them having zero civilian oversight (hell, the only oversight they have is the grim specter of death itself). It's why they are so butt-hurt over Kavanaugh; he represented the last best chance the Democrats had to flip the court to serve as their own private firewall, taken from them.
It's part of the deal made between McConnell and Trump, which circumvented the more quisling House GOP members who were scared of the DNC machine lynching them along with Trump to truly 100% support Trump. McConnell gets the Senate to support Trump completely, in exchange for Trump supporting McConnell's own agendas and expediting the filling of all of the open Judgeships ASAP. McConnell tacitly knows he's got four years minimum to fill as many seats as he can and as part of the vetting, these judges are made aware they have to support Trump's own agenda too when it comes before them.
And neutering the Senate filibuster is one of those things BOTH sides have long been wary about doing BECAUSE it leads to stuff like McConnell now being able to move faster than he normally would be able to move to fill those spots.
And this goes under reported for the most part, because A. it's not sexy enough for the media and B. if the lunatic left KNEW about it, they'd all be slitting their wrists in existential despair at how badly they've lost the long game.